146 J. Croll— Cause of Mild Polar Climates. 
Miocene period.”* That Prof. Nordenskjéld may not have seen 
in those strata bowlders larger than a child’s head may be 
perfectly true, but that there actually are none is a thing utterly 
incredible. Still more incredible, however, is the conclusion 
which he draws from this absence of bowlders, viz: that from 
vegetation. Perhaps the same skill and indomitable perse 
verance which proved the one conclusion to be erroneous may 
yet one day prove the other to be also equally erroneous. 
Professor Nordenskjéld does not appear to believe in alterna 
tions of climate even in temperate regions, for he says “from 
palseontological science no support can be obtained for the 
assumption of a periodical alternation of warm and cold 
climates on the surface of the earth.” | 
Evidence of Glaciation during the Tertiary period.—Evidence 
of glaciation during the Miocene period is, I think, afforded 
by the well-known conglomerates and erratics near Turin, first 
* Geological Magazine, 1875, p. 531. 
